This invention relates generally to infrared imaging apparatus. More particularly, the invention concerns a manually portable instrument capable of high-resolution, two-dimensional infrared imaging of a remote target.
Commercial thermographic products are rooted in the military technologies developed for night vision, reconnaissance and targeting, in which the real-time imagery of moving targets is made possible by complex, costly apparatus that use exotic materials, multi-element detector arrays and cryogenic cooling to achieve high-resolution, flicker-free infrared images. Such complex opto-electronic systems impose a maintenance burden that few commercial users are able or willing to bear.
Many commercial applications for thermographic products have vastly simpler requirements. Frequently, the infrared imaging subject, or target, is stationary or may be constrained to remain so for several seconds. The infrared imaging apparatus most often is stationary. The production of a `snapshot`, or single frame, infrared image every few seconds, rather than many times per second, would satisfy most commercial users. Notwithstanding the less demanding environments of many commercial applications, most commercial users require high-quality, two-dimensional thermographic imaging, which may be characterized as having resolution that rivals the resolution of the most costly military products.
One commercial application in which the seemingly incongruous goals of low-cost, manually portable, high-resolution infrared imaging must be met is the thermal fault analysis of electronic circuit boards on the design bench, on the manufacturing floor or in the field. Such instrumentation must be capable of producing a high-resolution, two-dimensional, colorable, thermal image of a remote (noncontacting) target; it must be compact enough to be manually portable, while durable enough to withstand the harsh treatment that portability invites; and it must require only minimal calibration and preventive maintenance.
Accordingly, it is a principal object of the present invention to provide high-resolution infrared imaging apparatus in a manually portable instrument.
Another important object is to provide apparatus capable of producing an integral, color mappable, two-dimensional pixel image that may be stored, manipulated, displayed and telecommunicated over conventional data communication channels.
A further object of the invention is to provide a flexibly positionable infrared, optical subsystem that requires no cryogenic cooling.
Yet another object is to provide apparatus having a minimal number of optical devices requiring critical alignment.
Another important object of the invention is to provide apparatus that is highly tolerant of the slight opto-mechanical misalignments that may result from the ordinary use of manually portable instruments.
The apparatus of the invention combines, in what is referred to as an on-axis, optical subsystem, a single, reciprocably rotating, single-faceted, planar scanning mirror; a spherically concave converging mirror; and a single-element, non-cryogenically cooled, heat-sensitive element as means for detecting, pixel by pixel, the thermal radiation of a remote target. Image forming means includes a preamplifier circuit, a microprocessor and a frame memory in which a composite, two-dimensional, pixel representation of the thermal profile of the target is stored. Conventional, color mappable display means provides a visible image representative of the temperature of the target. The microprocessor also provides control for the drive motors that reciprocate the scanning mirror and, in the preferred embodiment of the invention, further provides a communication path, via a conventional data communications channel, to optional, remote data communications equipment.
In the preferred embodiment of the invention, the scanning mirror is reciprocable about two orthogonal axes, one of which is collinear with the focal axis of the converging mirror. Conventional stepper motors are used to reciprocate the scanning mirror in a raster, or so-called "flying spot" scan of the target. The lead selenide (PbSe) detector is located at the focal point of the converging mirror, and `behind` the scanning mirror (on the side of the scanning mirror opposite the converging mirror), a central region of which is transmissive, rather than reflective, of the infrared energy directed by the converging mirror toward the detector.
Infrared energy emanating from the target and along a line-of-sight axis from the target to the scanning mirror is reflected thereby onto the reflective surface of the converging mirror, from which it is directed through the transmissive region of the scanning mirror and focused on the detector. The detector produces a signal representative of the infrared radiation of the target at sequential, elemental, pixel locations thereacross. A preamplifier circuit and an analog to digital converter (ADC) condition the signal for digital presentation to the microprocessor, which processes the data based upon its monitoring and controlling of the instantaneous position of the stepper motors.
A housing in which the optics, or optical subsystem, is flexibly tripod-mounted may be located at some distance from the instrument containing the electronics and display monitor. Alternatively, the housing may be secured to the end of a flexibly positionable, articulated arm which extends from the portable instrument and provides for the positioning and orientation of the optics relative to the target. In a proposed modification, a parabolic converging mirror is used. In yet another, the detector interposes the converging mirror and the scanning mirror.
Thus, the objects of the invention are achieved: a manually portable instrument provides for the high-resolution, infrared imaging of remote targets by the use of an on-axis, optical system that is highly tolerant of inadvertent misalignment. The combination of non-cryogenically cooled, single-element detection; conventional stepper motor reciprocation of a flying spot scanning mirror; and digital motor control and data manipulation enable unprecedented low-cost, high-performance, infrared imaging.
These and other objects and advantages of the present invention more clearly will be understood from a consideration of the drawings and the following description of the preferred embodiment.